The present disclosure relates to satellites and more particularly to an improved waste heat removal system for spacecraft, including satellites.
The thermal control systems used in geostationary satellites (satellites using a geosynchronous orbit and commonly referred to as GEO satellites) typically rely on north and south facing panels to reject most of their waste heat and maintain thermal balance. For many GEO satellites, the capacity of these north/south thermal radiators is a key design driver that often serves to limit the overall satellite's capacity. Consequently, improvements in the efficiency of these heat removal systems can significantly improve overall satellite design capabilities and capacity. Furthermore, in order to maximize satellite design applicability and competitiveness, there is a need to do this in a modular and cost efficient manner.
Differential solar illumination as a function of inclination of the earth's axis towards the sun (the seasons) drives thermal radiator inefficiency. Specifically, during the half year centered about the summer solstice, a GEO satellite's north panel is heated by the sun and the south panel is in shadow. Likewise, during the half year centered about the winter solstice, a GEO satellite's south panel is heated by the sun while the north panel is in shadow. A thermal mapping of the spacecraft shows distinct temperature differentials between the north and south radiator panels on a satellite. The differences are a direct result of the solar conditions relative to the GEO satellite orbit.
This seasonal aspect of GEO satellite solar heating drives the basic sizing and capacity of a spacecraft's primary thermal radiators. Specifically, the north thermal radiator is sized to maintain all north panel components within its operational temperature limits when the panel is hottest, i.e. during the summer solstice. The south panel is likewise designed for winter solstice conditions. As such, north and south thermal radiator panels typically have excess thermal capacity for all but the worst case times of the year. This excess capacity is inefficient. The magnitude of the inefficiency is a function of how well the satellite's thermal system can transport heat between the north and south radiator panels.
As power capability requirements for spacecraft increase, spacecraft thermal dissipation requirements will continue to grow and future satellite designs will require greater thermal dissipation capacity.
Accordingly, it is desirable to exploit the seasonal excess thermal capacity by providing a cost effective modular system suitable for use on multi-mission satellite platforms that must accommodate payloads with varying equipment complements and dissipation requirements.